BACKGROUND AND METHODS: We have investigated the cellular events underlying the development of effector T lymphocytes. The strategy was to separate the initial induction of sensitization by antigen from subseqent cell movement and differentiation. The aim was to see how the immune system responded to sensitized syngeneic lymphocytes, as distinct from antigen itself. Initiator T lymphocytes (ITL) were sensitized in vitro by culture with fibroblasts or with syngeneic macrophages that had been pulsed with specific antigens. Sensitized ITL were collected from the sensitizing cultures and then injected into the footpads of syngeneic mice. The sensitized ITL migrated to the draining popliteal lymph node (PLN). These ITL did not become effector cells, but trapped other cells from the circulation of the recipient into the PLN. The trapped recipient cells were recruited T lymphocytes (RTS). These RTL gave rise to specific effector and memory lymphocytes. Thus, the generation of effector cells involved the sequential interaction of macrophages, ITL and RTL. OBJECTIVES: 1. Characterization of these cellular interactions; including cell classes, genetic requirements and distribution and migration of the cells in the immune system. 2. The results of these basic studies will be applied to facilitate development of effector and memory lymphocytes capable of rejecting syngeneic metastatic tumor cells.